From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-0.3 required=5.0 tests=BAYES_00,
	REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no version=3.4.4
X-Google-Thread: 103376,99e73f65ea2533b9
X-Google-Attributes: gid103376,domainid0,public,usenet
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news1.google.com!news1.google.com!Xl.tags.giganews.com!border1.nntp.dca.giganews.com!nntp.giganews.com!local02.nntp.dca.giganews.com!nntp.bt.com!news.bt.com.POSTED!not-for-mail
NNTP-Posting-Date: Thu, 04 Sep 2008 17:02:51 -0500
From: Brian Drummond <brian_drummond@btconnect.com>
Newsgroups: comp.lang.ada
Subject: Re: and then... (a curiosity)
Date: Thu, 04 Sep 2008 23:09:02 +0100
Reply-To: brian@shapes.demon.co.uk
Message-ID: <fsm0c41mv7ubhp3j6ervvurk1ns0btcmsl@4ax.com>
References: 
 <18b41828-bda4-4484-8884-ad62ce1c831d@f36g2000hsa.googlegroups.com>
 <874p53bij6.fsf@willow.rfc1149.net>
 <94cc1ce3-59d1-41fa-9167-f3b60ddd2835@a1g2000hsb.googlegroups.com>
 <48bba264$1@news.post.ch> <ufxojoimh.fsf@STRIPCAPStelus.net>
 <48bce306$1@news.post.ch> <utzcyldk4.fsf@STRIPCAPStelus.net>
 <wccljya6zmt.fsf@shell01.TheWorld.com>
 <ta0tb49oskm9q51i7orteuekqf9qmfrhs0@4ax.com>
 <wcctzcxgr4w.fsf@shell01.TheWorld.com>
X-Newsreader: Forte Agent 1.7/32.534
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
X-Usenet-Provider: http://www.giganews.com
X-AuthenticatedUsername: NoAuthUser
X-Trace: 
 sv3-YVyYIqPKPFrDjI86NY4H60cJPDiS2G5ptFl48hRf75iuH66hrs223VcUfLM64lWsMqP3cgsYcU+krRe!cHBDhScFIUQ8hba3KlylMvjySX9vltbWzWGwGnhoLrNJPjTZad9hasvIn6koxt/u79jgLH+MMGNt!Gg==
X-Complaints-To: abuse@btinternet.com
X-DMCA-Complaints-To: abuse@btinternet.com
X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers
X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint
 properly
X-Postfilter: 1.3.39
Xref: g2news1.google.com comp.lang.ada:1930
Date: 2008-09-04T23:09:02+01:00
List-Id: <comp.lang.ada>

On Wed, 03 Sep 2008 11:56:15 -0400, Robert A Duff
<bobduff@shell01.TheWorld.com> wrote:

>Brian Drummond <brian_drummond@btconnect.com> writes:

>> But it does illustrate that (I) "and then" (short circuit form, order
>> guaranteed) and (II) "and" (short circuit permitted, but not guaranteed,
>> order not guaranteed) are properly separate operations.
>>
>> For cases such as the logging example (semantics require both to be
>> evaluated) my personal choice would be to explicitly evaluate both, and
>> combine their evaluation results, as elsewhere in this thread. 
>>
>> Is my understanding of Ada correct in expecting this is the only way to
>> guarantee evaluation of both? ( i.e. Ada handles "and" as (II) above)
>
>No.  Ada guarantees that both arguments of "and" are evaluated.
>Of course if the compiler knows that evaluation has no effect, it
>doesn't need to generate any code -- that would be the case for
>"X > 0", for example. 

In the process it must give up some opportunities for optimisation
(though I suspect, not as many as e.g. mandating the short-circuit form
in a particular order). 
Note: I am not complaining that this is an unreasonable design decision.

- Brian